During the running process of an automobile, lubricating oil is required to be supplied to various components timely to guarantee the normal operation of the automobile. If the lubricating performance of the lubricating oil is not good enough, the service life of the automobile will be affected, and even a traffic accident may be caused. The lubricating performance of the lubricating oil is significantly associated with its temperature, and the lubricating performance of the lubricating oil will be affected when the temperature of the lubricating oil is too high or too low.
During the normal operation of the automobile, the temperature of the lubricating oil generally won't be too high, and when the automobile runs under overload, runs on a snowfield or runs off-road in a four-wheel driving mode, or runs when a hydraulic torque converter slips excessively, the temperature of the transmission oil is exceeded, thus losing the lubricating performance.
Conventionally, the temperature of the transmission oil is mainly regulated by a cooling flow path composed of a thermostatic valve and an oil cooler. When the temperature of the transmission oil rises, a thermosensitive substance in a thermostatic actuating element is heated to expand, a passage which allows the transmission oil directly flows back into the transmission is closed, and the high-temperature oil flows into the oil cooler to be cooled and then flows back to the transmission. When the temperature of the oil is too low, the thermosensitive substance in the thermostatic actuating element is solidified and contracted, a piston is reset, and the passage which allows the transmission oil directly flows back into the transmission is opened. During the flowing process, the oil in the transmission oil path exchanges heat with heat-generating components in the transmission, thus the temperature of the oil gradually rises, and the thermosensitive substance of the thermostatic valve gradually expands to control the flow of the oil.
If the thermostatic valve is not provided, the passage for the transmission oil flowing into the oil cooler is always opened, which may increase oil consumption under low temperature and affect the service life of the transmission. Hence, in practical application, when the temperature of oil is lowered to a certain extent, it is not desirable that the transmission oil enters into the oil cooler, or only a few of transmission oil is allowed to enter into the oil cooler. The situation that oil enters into the oil cooler when a flow path of cooling liquid is blocked is referred to as an internal leakage. In the conventional technology, the pressure inside the oil cooler is used to prevent the transmission oil from entering into the oil cooler. Due to differences between various systems, the requirements on the internal leakage of the thermostatic valve are different, and the internal leakage degree of the existing thermostatic valve cannot meet the requirements in the practical application in some cases.